1. Field of the Invention
The present invention relates to a process for producing cyclopropanecarbonitrile.
2. Discussion of the Background
Cyclopropanecarbonitrile is useful as a material for producing aminophenylketones, which in turn can be used to produce sulfamoylurea herbicides, which are well-known herbicides applied to paddy-rice plants (See, Japanese Patent Laid-Open Publication No. Hei 7-188132 (188132/1995)).
Conventional processes for producing cyclopropanecarbonitrile include (1) a process as described in U.S. Pat. No. 3,853,942 and U.S. Pat. No. 5,380,911 that involves intramolecular cyclization of halobutyronitrile using a base, and (2) a process as described in U.S. Pat. No. 5,502,234 that involves converting cyclopropanecarbaldehyde into cyclopropanecarbaldoxime, which in turn is dehydrated using formic acid to form cyclopropanecarbonitrile, and neutralizing the resulting reaction mixture with an alkali metal compound.
However, the process (1) has a disadvantage that synthesis of halobutyronitrile, such as 4-chlorobutyronitrile, requires the use of expensive bromochloropropane, and nitrilization of bromochloropropane requires the use of toxic cyanogen compounds. On the other hand, in the process (2), the reaction mixture needs to be neutralized, following the dehydration, with an alkali metal compound and leads to the problem of the disposition of waste water containing alkali metal salt of formic acid as by-product formed in the process in abundance.
Accordingly, it is an object of the present invention to provide a process for producing cyclopropanecarbonitrile that can produce cyclopropanecarbonitrile in good yields in a safe, economical, and industrially advantageous manner.
In one aspect, the present invention provides a process for producing cyclopropanecarbonitrile, which is characterized in that cyclopropanecarbaldoxime is reacted with acetic anhydride.
In another aspect, the present invention provides a process for producing cyclopropanecarbonitrile that involves reacting cyclopropanecarbaldoxime with acetic anhydride to obtain a mixture containing acetic acid and cyclopropanecarbonitrile, and removing acetic acid from the mixture through azeotropic distillation of acetic acid with a solvent that forms with acetic acid an azeotropic mixture having an azeotropic point lower than the boiling point of the cyclopropanecarbonitrile.
In a preferred embodiment of the present invention, the above-mentioned removal of acetic acid through azeotropic distillation is achieved by using a hydrocarbon that forms with acetic acid an azeotropic mixture having an azeotropic point lower than the boiling point of the cyclopropanecarbonitrile.
Cyclopropanecarbaldoxime for use in the present invention can be readily produced by, for example, reacting cyclopropanecarbaldehyde with hydroxylamine. In the present invention, cyclopropanecarbaldoxime produced through the above-mentioned process may be used in the form of either a reaction mixture without purification or a purified product. When cyclopropanecarbaldoxime is to be used in the form of a reaction mixture, it is preferred to remove water from the reaction mixture through azeotropic distillation of water using a solvent, such as toluene, that forms an azeotropic mixture with water, in order to increase the reaction rate. Cyclopropanecarbaldoxime has two isomers, namely, a cis-form and a transform, which may be used independently or as a mixture of the two in the present invention.
The molar amount of acetic anhydride used in the present invention is preferably from 0.5 to 20 times, more preferably from 1 to 5 times, as much as that of cyclopropanecarbaldoxime.
The reaction of the present invention may be carried out in the presence or in the absence of a solvent. Examples of the solvent include aliphatic or aromatic hydrocarbon solvents such as hexane, heptane, octane, 2,5-dimethylhexane, cyclohexane, methylcyclohexane, toluene, xylene, ethylbenzene, styrene and cumene; halogenated hydrocarbon solvents such as chlorobenzene, 1,2-dichloropropane, 1,2-dibromopropane, butyl bromide, 1-bromo-3-methylbutane, propyl iodide and isobutyl iodide; ether solvents such as diethyl ether, isopropyl ether, t-butyl methyl ether and 1,4-dioxane; nitroethane and 1-butanol. Of these, the aliphatic or aromatic hydrocarbon solvents such as hexane, heptane, octane, toluene, xylene, ethylbenzene and cumene are preferred. The amount in mass of the solvent, if used, is preferably 50 times as much as that of cyclopropanecarbaldoxime or less, and more preferably from 1 to 10 times as much as that of cyclopropanecarbaldoxime. The reaction may be carried out either in a solution or in a slurry.
The reaction is preferably carried out at a temperature of 50 to 120xc2x0 C., more preferably 80 to 110xc2x0 C., in consideration of the reaction rate and selectivity. Preferably, the reaction time is from about 3 to about 20 hours.
While cyclopropanecarbonitrile can be isolated from the resulting reaction mixture by simply distilling the reaction mixture, but it is preferred in one embodiment of the present invention that a solvent that forms with acetic acid an azeotropic mixture having an azeotropic point lower than the boiling point of cyclopropanecarbonitrile is added to the above-mentioned reaction mixture and the resulting mixture is distilled to remove acetic acid based on the principle of azeotropic distillation first. Subsequently the remaining mixture is distilled to obtain cyclopropanecarbonitrile. Examples of the solvent that forms with acetic acid an azeotropic mixture having an azeotropic point lower than the boiling point of cyclopropanecarbonitrile include aliphatic or aromatic hydrocarbon solvents such as hexane, heptane, octane, 2,5-dimethylhexane, cyclohexane, methylcyclohexane, toluene, xylene, ethylbenzene, styrene and cumene; halogenated hydrocarbon solvents such as chlorobenzene, 1,2-dichloropropane, 1,2-dibromopropane, butyl bromide, 1 -bromo-3-methylbutane, propyl iodide and isobutyl iodide; 1,4-dioxane; nitroethane and 1-butanol. Of these, the aliphatic or aromatic hydrocarbon solvents such as hexane, heptane, octane, toluene, xylene, ethylbenzene and cumene are particularly preferred in consideration of effects on environment and safety.
When the reaction of cyclopropanecarbaldoxime with acetic anhydride is carried out in the presence of the above-mentioned solvent, the generated acetic acid can be removed by taking advantage of the principle of azeotropic distillation as the reaction progresses.
While the removal of acetic acid based on azeotropic distillation can be carried out under normal pressure, if necessary, it may be carried out under reduced pressure. In such a case, the temperature of the system may vary depending on the pressure, but it is preferably maintained in the range of 40 to 120xc2x0 C., more preferably in the range of 80 to 110xc2x0 C.
After the removal of acetic acid, cyclopropanecarbonitrile can be isolated and/or purified from the reaction mixture remaining by using a common technique for isolating and/or purifying an organic compound, for example, distillation under reduced pressure. The purity of cyclopropanecarbonitrile can be readily increased in this manner.
According to the present invention, cyclopropanecarbonitrile can be produced in good yields, in a safe, economical, and industrially advantageous manner.